As the technology of surface mounting electronic components to substrates continues to gain acceptance in today's marketplace and continues to find preference over through-hole circuit board assembly, ceramic multi-layer capacitors are increasing in popularity at the expense of polymer dielectric capacitors. Prior art polymer dielectric capacitors, in order to be suitable for surface mounted applications, must be thermally protected. However, such thermal protection renders the polymer dielectric capacitors larger in size and more expensive than similarly valued ceramic multi-layer capacitors. The ceramic multi-layer capacitor, if not thermally shocked, will withstand high temperature solder assembly techniques to substrates. In such high temperature solder assembly situations, a ceramic multi-layer capacitor's value will shift upward with the temperature rise during soldering and then exponentially decay over a period of days with the rate of decay depending upon the specific ceramic body involved. Ceramic capacitors, since they are subjected to extremely high temperatures during their manufacture, do not require an insulated overcoat to protect them thermally so that they are small and their cost is kept low.
It is well known in the electronics industry that polymer dielectric capacitors, commonly known as plastic film capacitors, enjoy some important advantages over ceramic multi-layer capacitors. For example, insulation resistance, a measure of the capacitor's resistance to providing a leakage path, is generally higher with plastic film capacitors than with similarly valued and dimensioned ceramic multi-layer capacitors.
Further, the dissipation factor, a factor relating to the dissipation of energy by a capacitor, is generally lower with plastic film capacitors than with similarly valued and dimensioned ceramic multi-layer capacitors.
Of perhaps the greatest importance is the capability of plastic film capacitors to self-heal in the event of a short circuit. Plastic film capacitors are coated with thin metal electrodes (generally aluminum) which electrodes vaporize at a shorted area to instantly clear the short and self-heal. Ceramic multi-layer electrodes are thick film and will not vaporize and clear. As a result, the ceramic multi-layer parts, when shorted, can dissipate a large amount of energy, which energy is sometimes manifested as heat sufficient to start fires within equipment.
Thus, it would be of extreme value to the electronic industry if a plastic film capacitor, with all of its advantages over ceramic multi-layer capacitors, could be produced which could withstand the rigors and the elevated temperatures of automated soldering techniques employed in surface mounting of electronic components in high volume production operations.
The present invention is directed to a method for manufacturing just such a plastic film capacitor, capable of being surface mounted upon a substrate using automated soldering techniques presently known in the industry, which soldering techniques involve temperatures significantly higher than it was previously thought possible to apply to plastic film capacitors.